With regard to the widespread introduction of video telephony, telecommunications network operators wish to offer the high quality and high user convenience that is known from public telephony networks and cable TV networks. As a rule, however, this cannot be achieved via networks operating an Internet protocol. To satisfy these requirements requires the development of solutions using set-top boxes connected by hardwired modem or xDSL to TV sets rather than PCs. This makes it easy and convenient to convert from TDM to IP using little more than the video bandwidth option and TV remote control. In addition, the quality of service (availability, transmission quality, freedom from interference, etc.) and the security aspects have to be the same as those already known from the public network. Of special interest to customers in this regard is the fair, detailed and comprehensible billing system which is known from public telephone networks, and which must without fail include time-based billing for the purpose of correct implementation.
Time-based billing is already known from the TDM world. This provides TDM channels that are routed into the switching center. Billing in the switching center, for example for each channel, then takes place for as long as the connection lasts. Interference is therefore directly detected and the connections concerned are released immediately. When the connections are released billing is also stopped. Though this approach would be suitable for audio and video via TDM (where the number of channels determines the quality and charge), it cannot be used in a packet network.
This is because in packet-oriented connections, such as those routed via IP networks, the useful data stream is preferably routed directly between the subscribers concerned rather than through the switching center. As a rule, any network failures that interrupt said useful data stream are not directly detected in the packet-based switching centers responsible for the connection. Billing therefore continues to run, even though the useful data stream has already been interrupted. The connection cannot be released and billing cannot be stopped until the network interference is disclosed via the signaling. A signaling path is rarely disturbed at the same time as the useful data path, since signaling data and useful data are routed via different paths and links.
Furthermore a signaling loss that occurs in the stable call state cannot be detected without further measures, since no signaling messages are exchanged in this state. As a rule, a loss of useful data transmission is detected in the terminal devices or quasi-terminal devices, which then inform the packet-based switching center via signaling. However, this can be delayed and is not reliable, since the signaling path could be experiencing interference at the same time.
For these reasons, in the case of packet-based connections in which the useful data stream is routed directly between subscribers or their terminal devices via a packet network, billing is preferably provided on a flat rate basis or per event (polling a proxy to establish a connection). Although this approach is very simple and suitable for packet networks, it cannot be described as exact billing with regard to duration, volume or quality.
It has therefore been proposed in the prior art that when the useful data stream is directly routed between subscribers or terminal devices via the packet network, billing should be performed on a time basis in the A-side link node. On a cyclical basis the A and B-side link nodes check whether each connected port is available for signaling. A cyclical value of 20 s is typically used. Any connection found to be unavailable is released in order to stop the billing. Although this approach is very simple and suitable for packet networks, it cannot be said to achieve exact billing with regard to duration, volume or quality. Furthermore the polling load on the link nodes and network seems to be a serious disadvantage. The volume and quality of the connection are not taken into consideration.
As a result of this problem the subscriber is overcharged in the event of a failure or interference. However, the subscriber can easily check the billing accuracy from the itemized bill. Any overcharge for a connection that the customer knows to have been disrupted is disclosed in the corresponding itemized bill from the network operator. The network operator may then receive complaints or even become involved in legal disputes with the customer.